Rare-earth pre-alloyed PVD targets for dielectric planar applications

ABSTRACT

A target material for deposition of rare-earth doped optical materials is described. The rare-earth ions, for example erbium and ytterbium, is prealloyed with host materials. In some embodiments a ceramic target material can be formed by pre-alloying Er 2 O 3  and/or Yb 2 O 3  with Al 2 O 3  and/or SiO 2 . In some embodiments, a metal target material can be formed by pre-alloying Er and/or Yb with Al and/or Si. In some embodiments, ceramic or metallic tiles are formed which can be mounted on a backing plate. In some embodiments, an intermetallic mixture can be formed and flame sprayed onto the backing plate.

BACKGROUND

[0001] 1. Field of the Invention

[0002] This invention relates to deposition of doped oxide materials and, in particular, to a target for physical vapor deposition (PVD) of, for example, rare-earth doped oxide materials.

[0003] 2. Discussion of Related Art

[0004] Deposition of insulating materials and especially optical materials is technologically important in several areas including production of optical devices and production of semiconductor devices. In semiconductor devices, doped alumina silicates can be utilized as high dielectric insulators.

[0005] The increasing prevalence of fiber optic communications systems has created an unprecedented demand for devices for processing optical signals. Planar devices such as optical waveguides, couplers, splitters, and amplifiers, fabricated on planar substrates, like those commonly used for integrated circuits, and configured to receive and process signals from optical fibers are highly desirable. Such devices hold promise for integrated optical and electronic signal processing on a single semiconductor-like substance.

[0006] The basic design of planar optical waveguides and amplifiers is well known, as described, for example, in U.S. Pat. Nos. 5,119,460 and 5,563,979 to Bruce et al., U.S. Pat. No. 5,613,995 to Bhandarkar et al., U.S. Pat. No. 5,900,057 to Buchal et al., and U.S. Pat. No. 5,107,538 to Benton et al., to cite only a few. These devices, very generally, include a core region, typically bar shaped, of a certain refractive index surrounded by a cladding region of a lower refractive index. In the case of an optical amplifier, the core region includes a certain concentration of a dopant, typically a rare earth ion such as an erbium or praseodymium ion which, when pumped by a laser, fluoresces, for example, in the 1550 nm and 1300 nm wavelength ranges used for optical communication, amplify the optical signal passing through the core.

[0007] As described, for example in the patents by Bruce et al., Bhandarkar et al, and Buchal et al., planar optical devices may be fabricated by process sequences including forming a layer of cladding material on a substrate; forming a layer of core material on the layer of cladding mater; patterning the core layer using a photolighotgraphic mask and an etching process to form a core ridge; and covering the core ridge with an upper cladding layer.

[0008] The performance of these planar optical devices depends sensitively on the value and uniformity of the refractive index of the core region and of the cladding region, and particularly on the difference in refractive index, Δn, between the regions. Particularly for passive devices such as waveguides, couplers, and splitters, Δn should be carefully controlled, for example to values within about 1%, and the refractive index of both core and cladding need to be highly uniform, for some applications at the fewer than parts per thousand level. In the case of doped materials forming the core region of planar optical amplifiers, it is important that the dopant be uniformly distributed so as to avoid non-radiative quenching or radiative quenching, for example by upconversion. The refractive index and other desirable properties of the core and cladding regions, such as physical and chemical uniformity, low stress, and high density, depend, of course, on the choice of materials for the devices and on the processes by which they are fabricated.

[0009] Because of their optical properties, silica and refractory oxides such as Al₂O₃ are good candidate materials for planar optical devices. Further, these oxides serve as suitable hosts for rare earth dopants used in optical amplifiers. A common material choice is so-called low temperature glasses, doped with alkali metals, boron, or phosphorous, which have the advantage of requiring lower processing temperatures. In addition, dopants are used to modify the refractive index. Methods such as flame hydrolysis, ion exchange for introducing alkali ions in glasses, sputtering, and various chemical vapor deposition processes (CVD) have been used to form films of doped glasses. However, dopants such as phosphorous and boron are hygroscopic, and alkalis are undesirable for integration with electronic devices. Control of uniformity of doping in CVD processes can be difficult and CVD deposited films can have structural defects leading to scattering losses when used to guide light. In addition, doped low temperature glasses may require further processing after deposition. A method for eliminating bubbles in thin films of sodium-boro-silicate glass by high temperature sintering is described, for example, in the '995 patent to Bhandarkar et al.

[0010] Generally, when films are sputtered onto a target, the rare-earth ions in the target may form aggregates of two or more adjacent ions. These aggregates degrade the performance of the material layer that has been deposited. Several conventional targets have been formed with mixtures of Al₂O₃ and/or SiO₂, Er₂O₃ and/or Yb₂O₃ by sintering and hot pressing. Aggregates of erbium in the deposited material, for example, are detrimental due to up-conversion processes. In an Er-doped amplifier, for example, the Er ion radiative coupling processes (e.g., pair induced quenching, up-conversion), which results from Er clusters and Er pairing, is well known to result in inefficient amplification.

[0011] In erbium doped amplifiers, for example, an erbium concentration of 0.3% (about 1×10²⁰/cm³) results in erbium ion separations of about 22 angstroms if they are uniformly spaced, which is about 10 bond lengths. An ideal erbium concentration of about 1% (about 3×10²⁰/cm³), results in a separation of about 14 angstroms or about 5-6 bond lengths. A 0.1% erbium concentration results in a 32 angstroms separation. It is extremely difficult to prevent the erbium ions from pairing or clustering during deposition. Additionally, in many target designs the erbium ions may aggregate in the target material before deposition of the material layer and during deposition these ions may preferential deposit in pairs or larger clusters.

[0012] Another common problem in deposition is OH impurities, which serve to also quench the transitions required for pumping and amplification. Targets formed by sol-gel precipitation, for example, suffer from high OH impurities in the deposited material layer.

[0013] Additionally, target material can be formed from glass materials, see, e.g., M. P. Hehlen, N. J. Cockroft, T. R. Cosnell, A. J. Bruce, C. Nykolak, and J. Shmulovich, “Uniform Upconversion in High-Concentration Er³⁺-Doped Soda Lime Silicate and Aluminosilicate Glasses”, Optics Letters, Vol. 22, No. 1, p. 772 (1997), which may provide uniform non-aggregated rare-earth concentrations, but which are mechanically brittle. Further, glass targets usually have large concentrations of OH impurities, which degrade the optical properties of a deposited layer.

[0014] Further, billets for forming targets have been made by flame spraying Nd with Al, see, e.g., K. Yoshikawa, Y. Yoneda, and K. Koide, “Spray formed aluminum alloys for sputter targets,” Powder Metallurgy, Vol. 43, no. 3 p. 198 (2000). However, with higher Nd concentrations (e.g., greater than about 2% Nd), the Nd which has been alloyed with the Al during the flame spraying process precipitates out during the following HIPing process, resulting in clusters of Nd ions.

[0015] Depositions of material films typically utilize a target for sputtering of material onto a substrate. The material properties of the deposited film, therefore, directly depend on the material properties of the target. The deposition process and the materials utilized in the deposition process of optical insulating layers primarily determines the quality and performance of the resulting optical structures. Therefore, there is a desire to provide starting materials and targets for deposition processes that result in optical devices and insulating layers of high quality.

SUMMARY

[0016] In accordance with the present invention, a target for a Physical Vapor Deposition (PVD) process utilized for deposition of optical layers is described. A target according to the present invention is formed so that rare-earth dopants are pre-alloyed with the constituent host materials, resulting in more uniform deposition of dopants, less aggregation of the rare-earth impurities in the target and during deposition, and higher durability due to structure effects in the target. The alloyed compounds, then, also act as a sintering agent, producing physically more robust and durable target materials.

[0017] A target according to the present invention can include one or more individual tiles mounted on a backing plate. In some embodiments, each of the tiles can be formed in a hot isostatic press (HIP) process. Preparation of the starting materials for the HIPing process, and in some embodiments the HIPing process itself, results in alloying of rare-earth impurity ions. In some embodiments, a prealloyed starting material can be formed and that material deposited on the backing plate, for example by flame spraying a pre-alloyed and mixed powder to the backing plate.

[0018] In some embodiments, a ceramic tile can be fabricated in a HIP process. The process begins by mixing oxides, including the host oxides and oxides of rare-earth compounds. For example SiO₂, Al₂O₃, Er₂O₃ and Yb₂O₃ can be mixed in predetermined relative concentrations. In some embodiments, a total atomic percentage of up to about 10 cat % of rare earths can be utilized. The mixture can then be poured into a form and cold isostatic pressed (CIP), for example to a density approximately 50% that of the theoretical density. The pressed (“green”) mixture is then degassed at a high temperature, for example a temperature greater than about 550 C, in a vacuum. Finally, the degassed formed mixture is hot isostatically pressed, for example at temperatures less than about 1000° C. and at pressures of about 30 Kpsi. The resulting billet can then be machined and formed into individual tiles. The resulting tile includes compounds alloyed compounds of ErAlO₃ and YBSiO₅ and little to no free Er₂O₃ or Yb₂O₃.

[0019] In some embodiments, alloying of rare earth ions such as Er can be prealloyed in Al₂O₃ by melting a mixture containing erbium in an alumina crucible. The low melting temperature of the alumina crucible leads to alloying of the erbium into the Al₂O₃. In some embodiments, a prealloyed powder for a ceramic target can be formed in an Al₂O₃ crucible by e-beam melting of a solution of Al₂O₃, Er₂O₃, Yb₂O₃, and SiO₂, for example.

[0020] In some embodiments, a metallic target can be fabricated in a HIPing process. First, the atomic constituents can be atomized in an atomization process to form intermettalics, for example Al and/or Si and Er and/or Yb can be atomized. With Al, Er and Yb atomization, for example, the atomized powder includes AlEr₃, AlYb₃ and free aluminum. In some embodiments, there is substantially no free Er in the intermettalic mix. The intermettalics are then mixed. In some embodiments, further constituents, for example silicon, can be added before mixing. The resulting mixture can be poured into a mold and HIPed at low temperature, for example about 600 C, to form a billet. The billet can then be machined to form individual tiles.

[0021] In some embodiments, several tiles of target material, either ceramic or metallic as discussed above, can be formed and affixed to a backing plate to form a target. The target is then utilized in a physical vapor deposition (PVD) chamber to form material layers having composition and properties related to the composition and properties of the target. In some embodiments, the mixed intermettalics can be flame or plasma sprayed directly on a backing plate to form a target.

[0022] These and other embodiments are further discussed below with respect to the following figures.

SHORT DESCRIPTION OF THE FIGURES

[0023]FIGS. 1A and 1B show a diagram of a PVD process chamber with a target according to the present invention.

[0024]FIG. 2 shows a plan view of a target for a PVD process chamber according to the present invention.

[0025]FIG. 3A shows a cross-sectional view of a target for a PVD process chamber according to the present invention.

[0026]FIG. 3B shows a planar view of one embodiment of a target utilizing ceramic tiles according to the present invention.

[0027]FIG. 4A shows a phase diagram of Al₂O₃ with Er₂O₃.

[0028]FIG. 4B shows a phase diagram of Er and Al ions.

[0029]FIG. 4C illustrates a waveguide amplifier formed utilizing targets according to the present invention.

[0030]FIG. 5 illustrates manufacture of a ceramic tile for a target according to the present invention.

[0031]FIGS. 6A through 6F show x-ray diffraction data showing alloying of rare-earth pre-alloying in an embodiment of a ceramic target according to the present invention.

[0032]FIGS. 6G and 6H show electron dispersion data also showing alloying of Er and Yb with Al₂O₃ and SiO₂.

[0033]FIGS. 7A through 7D show x-ray diffraction data of another embodiment of a target according to the present invention showing alloying of rare earth ions.

[0034]FIG. 8A illustrate methods of producing a metallic tile for a metallic target according to the present invention.

[0035]FIG. 8B illustrates another method of producing a metallic target according to the present invention.

[0036]FIG. 9 shows an x-ray diffraction spectrum of alloyed powder utilized in an example embodiment of the present invention.

[0037]FIG. 10 shows x-ray diffraction spectrum of alloyed powder utilized in another example embodiment of the present invention.

[0038] In the figures, elements having the same designation have the same or similar functions.

DETAILED DESCRIPTION OF THE FIGURES

[0039] A physical vapor deposition (PVD) process provides layers of optical materials with controlled and uniform refractive index that can be utilized for active and passive planar optical devices. The process uses sputtering with a wide area target and a condition of uniform target erosion and includes multiple approaches for controlling refractive index. PVD processes which may utilize targets according to the present invention are described in application Ser. No. 09/903,050 (the '050 application) by Demaray et al., entitled “Planar Optical Devices and Methods for Their Manufacture,” assigned to the same assignee as is the present invention, herein incorporated by reference in its entirety. Further, PVD processes which may utilize targets according to the present invention are described in concurrently filed application U.S. Application Serial No. M-12245 US} (the '245 application), assigned to the same assignee as is the present invention, herein incorporated by reference in its entirety.

[0040]FIG. 1A shows a schematic of an apparatus 10 for sputtering of material from a target 12 according to the present invention. In some embodiments, controlled refractive index material for planar optical devices can be deposited with apparatus 10.

[0041] Apparatus 10 can include a wide area sputter source target 12, which provides material to be deposited on substrate 16. Substrate 16 is positioned parallel to and opposite target 12. Target 12 functions as a cathode when power is applied to it and is equivalently termed a cathode.

[0042] In some embodiments of the invention, target 12 can include pure materials such as quartz, alumina, or sapphire, (the crystalline form of alumina), mixtures of compounds of optically useful materials, or intermettalics. Optically useful materials include oxides, fluorides, sulfides, nitrides, phosphates, sulfates, and carbonates, as well as other wide band gap semiconductor materials. In some embodiments, target 12 includes a metallic target material formed from intermetalic compounds of optical elements such as Si, Al, Er and Yb. To achieve uniform deposition, target 12, itself can be chemically uniform, flat, and of uniform thickness over an extended area. Target 12 can be a composite target fabricated from individual tiles, precisely bonded together on a backing plate with minimal separation, as is discussed further with respect to FIG. 3A. In some embodiments, the mixed intermetalllics can be plasma sprayed directly onto a backing plate to form target 12. The complete target assembly can also includes structures for cooling the target, embodiments of which have been described in U.S. Pat. No. 5,565,071 to Demaray et al, and incorporated herein by reference.

[0043] Substrate 16 can be a solid, smooth surface. Typically, substrate 16 can be a silicon wafer or a silicon wafer coated with a layer of silicon oxide formed by a chemical vapor deposition process or by a thermal oxidation process. Alternatively, substrate 16 can be a glass, such as Corning 1737 (Corning Inc., Elmira, N.Y.), a glass-like material, quartz, a metal, a metal oxide, or a plastic material. Substrate 16 typically is supported on a holder or carrier sheet 17 that may be larger than substrate 16.

[0044] In some embodiments, the area of wide area target 12 can be greater than the area on the carrier sheet on which physically and chemically uniform deposition is accomplished. Secondly, in some embodiments a central region on target 12, overlying substrate 16, can be provided with a very uniform condition of sputter erosion of the target material. Uniform target erosion is a consequence of a uniform plasma condition. In the following discussion, all mention of uniform condition of target erosion is taken to be equivalent to uniform plasma condition. Uniform target erosion is evidenced by the persistence of film uniformity throughout an extended target life. A uniformly deposited film can be defined as a film having a nonuniformity in thickness, when measured at representative points on the entire surface of a substrate wafer, of less than about 5% or 10%. Thickness nonuniformity is defined, by convention, as the difference between the minimum and maximum thickness divided by twice the average thickness. If films deposited from a target from which more than about 20% of the weight of the target has been removed continue to exhibit thickness uniformity, then the sputtering process is judged to be in a condition of uniform target erosion for all films deposited during the target life.

[0045]FIG. 1B illustrates plasma conditions in apparatus 10. A uniform plasma condition can be created in the region between target 12 and substrate 16 in a region overlying substrate 16. The region of uniform plasma condition is indicated in the exploded view of FIG. 1B. A plasma 53 can be created in region 51, which extends under the entire target 12. A central region 52 of target 12, can experience a condition of uniform sputter erosion. As discussed further below, a layer deposited on a substrate placed anywhere below central region 52 can then be uniform in thickness and other properties (i.e., dielectric, optical index, or material concentrations).

[0046] In addition, region 52 in which deposition provides uniformity of deposited film can be larger than the area in which the deposition provides a film with uniform physical or optical properties such as chemical composition or index of refraction. In some embodiments, target 12 is substantially planar in order to provide uniformity in the film deposited on substrate 16. In practice, planarity of target 12 can mean that all portions of the target surface in region 52 are within a few millimeters of a planar surface, and can be typically within 0.5 mm of a planar surface.

[0047] Multiple approaches to providing a uniform condition of sputter erosion of the target material can be used. A first approach is to sputter without magnetic enhancement. Such operation is referred to as diode sputtering. Using a large area target with a diode sputtering process, a dielectric material can be deposited so as to provide suitably uniform film thickness over a central portion of an adjacent substrate area. Within that area, an area of highly uniform film may be formed with suitable optical uniformity. The rate of formation of films of many microns of thickness by diode sputtering can be slow for small targets. However, in the present method, using large targets, a disadvantage in speed of diode sputtering can be compensated by batch processing in which multiple substrates are processed at once.

[0048] Other approaches to providing a uniform condition of sputter erosion rely on creating a large uniform magnetic field or a scanning magnetic field that produces a time-averaged, uniform magnetic field. For example, rotating magnets or electromagnets can be utilized to provide wide areas of substantially uniform target erosion. For magnetically enhanced sputter deposition, a scanning magnet magnetron source can be used to provide a uniform, wide area condition of target erosion. Diode sputtering is known to provide uniform films.

[0049] As illustrated in FIG. 1A, apparatus 10 can include a scanning magnet magnetron source 20 positioned above target 12. An embodiment of a scanning magnetron source used for dc sputtering of metallic films is described in U.S. Pat. No. 5,855,744 to Halsey, et. al., (hereafter '744), which is incorporated herein by reference in its entirety. The '744 patent demonstrates the improvement in thickness uniformity that is achieved by reducing local target erosion due to magnetic effects in the sputtering of a wide area rectangular target. As described in the '744 patent, by reducing the magnetic field intensity at these positions, the local target erosion was decreased and the resulting film thickness nonuniformity was improved from 8%, to 4%, over a rectangular substrate of 400×500 mm.

[0050] A top down view of magnet 20 and wide area target 12 is shown in FIG. 2. A film deposited on a substrate positioned on carrier sheet 17 directly opposed to region 52 of target 12 has good thickness uniformity. Region 52 is the region shown in FIG. 1B that is exposed to a uniform plasma condition. In some implementations, carrier 17 can be coextensive with region 52. Region 24 shown in FIG. 2 indicates the area below which both physically and chemically uniform deposition can be achieved, where physical and chemical uniformity provide refractive index uniformity, for example. FIG. 2 indicates that the region 52 of target 12 providing thickness uniformity is, in general, larger than region 24 of target 12 providing thickness and chemical uniformity. In optimized processes, however, regions 52 and 24 may be coextensive.

[0051] In some embodiments, magnet 20 extends beyond area 52 in one direction, the Y direction in FIG. 2, so that scanning is necessary in only one direction, the X direction, to provide a time averaged uniform magnetic field. As shown in FIGS. 1A and 1B, magnet 20 can be scanned over the entire extent of target 12 which is larger than region 52 of uniform sputter erosion. Magnet 20 is moved in a plane parallel to the plane of target 12.

[0052] The combination of a uniform target 12 with area larger than the area of substrate 16 can provide films of highly uniform thickness. Further, the material properties of the film deposited can be highly uniform. The conditions of sputtering at the target surface, such as the uniformity of erosion, the average temperature of the plasma at the target surface and the equilibration of the target surface with the gas phase ambient of the process are uniform over a region which is greater than or equal to the region to be coated with a uniform film thickness. In addition, the region of uniform film thickness is greater than or equal to the region of the film which is to have highly uniform optical properties such as index of refraction, density, transmission or absorptivity.

[0053] As shown in FIG. 1A, apparatus 10 includes a power supply 14 for applying power to target 12 to generate a plasma in a background gas. Power supply 14 can be a pulsed DC source as is discussed in the '245 application or an RF source as is discussed in the '050 application. An RF power supply is conventionally operated at 13.56 MHz. Typical process conditions for RF sputter deposition include applying high frequency RF power in the range of about 500 to 5000 watts. Power supply 14 may include other sources of power as well.

[0054] An inert gas, typically argon, is used as the background sputtering gas. Additionally, with some embodiments of target 12, oxygen may be added to the sputtering gas. Other gasses such as N₂, NH₃, CO, NO, CO₂, halide containing gasses other gas-phase reactants can also be utilized. The deposition chamber can be operated at low pressure, often between about 0.5 millitorr and 8-10 millitorr. Typical process pressure is below about 2 millitorr where there are very few collisions in the gas phase, resulting in a condition of uniform “free molecular” flow. This ensures that the gas phase concentration of a gaseous component is uniform throughout the process chamber. For example, background gas flow rates in the range of about 30 to about 100 sccm, used with a pump operated at a fixed pumping speed of about 50 liters/second, result in free molecular flow conditions.

[0055] The distance d, in FIG. 1A, between target 12 and substrate 16 can, in some embodiments, be varied between about 4 cm and about 9 cm. A typical target to substrate distance d is about 6 cm. The target to substrate distance can be chosen to optimize the thickness uniformity of the film. At large source to substrate distances the film thickness distribution is dome shaped with the thickest region of the film at the center of the substrate. At close source to substrate distance the film thickness is dish shaped with the thickest film formed at the edge of the substrate. The substrate temperature can be held constant in the range of about −40° C. to about 550° C. and can be maintained at a chosen temperature to within about 10° C. by means of preheating the substrate and the substrate holder prior to deposition. During the course of deposition, the heat energy impressed upon the substrate by the process can be conducted away from the substrate by cooling the table on which the substrate is positioned during the process, as known to those skilled in the art. The process is performed under conditions of uniform gas introduction, uniform pumping speed, and uniform application of power to the periphery of the target as known to skilled practitioners.

[0056] The speed at which a scanning magnet 20 can be swept over the entire target can be determined such that a layer thickness less than about 5 to 10, corresponding roughly to two to four monolayers of material, is deposited on each scan. Magnet 20 can be moved at rates up to about 30 sec/one-way scan and typically is moved at a rate of about 4 sec/one-way scan. The rate at which material is deposited depends on the applied power and on the distance d, in FIG. 1A, between the target 12 and the substrate 16. For deposition of optical oxide materials, for example scanning speeds between about 2 sec/one-way scan across the target to 20-30 sec/scan provide a beneficial layer thickness. Limiting the amount of material deposited in each pass promotes chemical and physical uniformity of the deposited layer. With the typical process conditions, the rate of deposition of pure silica can be approximately 0.8 Å/kW-sec. At an applied RF power of 1 kW, the rate of deposition is 0.8 Å/sec. At a magnet scan speed that provides a scan of 2 seconds, a film of 1.8 Å nominal thickness is deposited.

[0057] A thickness of 2.4 Å can be associated with one monolayer of amorphous silica film. The impingement rate of process gas equivalent to a monolayer per second occurs at approximately 1×10⁻⁶ torr. The process gas may contain oxygen atoms ejected from the silica during sputtering in addition to the background inert gas. For typical process conditions near 1 millitorr, 4×10³ monolayers of process gas impinge on the film during the 4 second period of deposition. These conditions provide adequate means for the equilibration of the adsorbed sputtered material with the process gas, if the sputtered material has a uniform composition. Uniform, wide area target erosion is required so as to ensure that the adsorbed sputtered material has a uniform composition.

[0058] In some embodiments, a dual frequency sputtering process, in which low frequency RF power is also applied to the target, can be used. Returning to FIG. 1A, apparatus 10 includes RF generator 15, in addition to power supply 14 described previously. For RF sputtering, power supply 14 is a high frequency source, typically 13.56 MHz, while RF generator 15 can provide power at a much lower frequency, typically from about 100 to 400 kHz. Typical process conditions for dual frequency RF deposition include high frequency RF power in the range of about 500 to 5000 watts and low frequency RF power in the range of about 500 to 2500 watts where, for any given deposition, the low frequency power is from about a tenth to about three quarters of the high frequency power. The high frequency RF power is chiefly responsible for sputtering the material of target 12. The high frequency accelerates electrons in the plasma but is not as efficient at accelerating the much slower heavy ions in the plasma. Adding the low frequency RF power causes ions in the plasma to bombard the film being deposited on the substrate, resulting in sputtering and densification of the deposited film.

[0059] In addition, the dual frequency RF deposition process generally results in films with a reduced surface roughness as compared with single frequency deposition. For silica, films with average surface roughness in the range of between about 1.5 and 2.6 nm have been obtained with the dual frequency RF process. Experimental results for single and dual frequency deposition are further described in Example 4 below. As discussed in the co-filed, commonly assigned U.S. application Attorney Docket No. M-11522 US, (the '522 application) which is incorporated herein by reference, reducing surface roughness of core and cladding materials helps to reduce scattering loss in planar optical devices.

[0060] Further, the dual frequency RF process can be used to tune the refractive index of the deposited film. Keeping the total RF power the same, the refractive index of the deposited film tends to increase with the ratio of low frequency to high frequency RF power. For example, a core layer of a planar waveguide can be deposited by a dual frequency RF process, and the same target 12, can be used to deposit a cladding layer using a single frequency RF process. Introducing low frequency RF power in the core layer deposition process can therefore be used to provide the difference in refractive index between core and cladding layer materials.

[0061] It is particularly beneficial to further augment the single frequency or dual frequency RF sputtering process by additionally applying RF power to the substrate 16, using, for example, substrate RF generator 18. Applying power to the substrate, resulting in substrate bias, also contributes to densification of the film. The RF power applied to the substrate can be either at the 13.56 MHz high frequency or at a frequency in the range of the low frequency RF. Substrate bias power similar to the high frequency RF power can be used.

[0062] Substrate bias has been used previously to planarize sputter deposited quartz films. A theoretical model of the mechanism by which substrate bias operates, has been put forward by Ting et al. (J. Vac. Sci. Technol. 15, 1105 (1978)). When power is applied to the substrate, a so-called plasma sheath is formed about the substrate and ions are coupled from the plasma. The sheath serves to accelerate ions from the plasma so that they bombard the film as it is deposited, sputtering the film, and forward scattering surface atoms, densifying the film and eliminating columnar structure. The effects of adding substrate bias are akin to, but more dramatic than, the effects of adding the low frequency RF component to the sputter source.

[0063] Using the bias sputtering process, the film is simultaneously deposited and etched. The net accumulation of film at any point on a surface depends on the relative rates of deposition and etching, which depend respectively, on the power applied to the target and to the substrate, and to the angle that the surface makes with the horizontal. The rate of etching is greatest for intermediate angles, on the order of 45 degrees, that is between about 30 and 60 degrees.

[0064] The target and substrate powers can be adjusted such that the rates of deposition and etching are approximately the same for a range of intermediate angles. In this case, films deposited with bias sputtering have the following characteristics. At a step where a horizontal surface meets a vertical surface, the deposited film makes an intermediate angle with the horizontal. On a surface at an intermediate angle, there will be no net deposition since the deposition rate and etch rate are approximately equal. There is net deposition on a vertical surface.

[0065] Apparatus 10 may, for example, by adapted from an AKT-1600 PVD (400×500 mm substrate size) system from Applied Komatsu or an AKT-4300 (600×720 mm substrate size) system from Applied Komatsu may form the base reactor. The AKT-1600, for example, has three deposition chambers connected by a vacuum transport chamber. These Komatsu reactors can be modified such that power at one or more RF frequencies. In addition, a pulse-DC power supplies can be applied for purposes of pulsed DC power as described in the '245 application.

[0066] Power supplies 14 and 15 can, for example, include a 13.56 MHz supply operating between about 500 and about 5000 Hz, a second power supply for providing a lower frequency power to substrate 16, and/or a pulsed DC power supply. Target 12 can have an active size of about 675.70×582.48 by 4 mm in, for example, a AKT-1600 based system in order to deposit films on a substrate 16 that is about 400×500 mm. The temperature of substrate 16 can be held at between −50C and 500C. The distance between target 12 and substrate 16 can be between 4 and 6 cm. Process gas can be inserted into the chamber of apparatus 10 at a rate of between about 30 to about 100 sccm while the pressure in the chamber of apparatus 10 can be held at below about 2 millitorr. Magnet 20 provides a magnetic field of strength between about 400 and about 600 Gauss directed in the plane of target 12 and is moved across target 12 at a rate of less than about 20-30 sec/scan.

[0067] Therefore, any given process utilizing apparatus 10 can be characterized by providing the power supplied to target 12, the power supplied to substrate 16, the temperature of substrate 16, the characteristics and constituents of the reactive gasses, the speed of the magnet, and the spacing between substrate 16 and target 12.

[0068] A major factor in producing uniform films for use in optical amplifiers and in producing targets is the uniformity in chemical composition, to the level of the metallurgy utilized to form the powder mixtures, of target 12. In some embodiments, ceramic targets are formed from rare-earth oxides and host oxide materials. In some embodiments, metallic targets are formed from rare earth and metallic ions.

[0069] In ceramic targets, typical powder sizes are between tens and hundreds of microns. In the case of refractory oxide additions, rare earth additions can be pre-alloyed with the refractory oxides. Plasma spray, transient melting, induction melting, or electron beam melting may be utilized to form a pre-alloyed solid which is a solution or alloy of such materials. A powder can be formed from the pre-alloyed solid.

[0070]FIG. 4A shows a phase diagram of Al₂O₃ with Er₂O₃, for example. In the diagram, the designation C refers to cubic formed rare earth oxide, G refers to garnet, P refers to perovskite, and α refers to corundum. The 2:1 phase refers to Er₄Al₂O₉, the 1:1 phase refers ErAlO₃, and the 3:5 phase refers to Er₃Al₅O₁₂. As can be seen in the phase diagram of FIG. 4A, Er₂O₃ and Al₂O₃ readily dissolve and form compounds with each other.

[0071] In the case of mixed materials containing alumina, for example, the low sputter yield of pure alumina can lead to segregation of the target material during sputtering. This causes the film to be low in aluminum with respect to the alloy target composition. It also can lead to particle production from the cathode. The high solubility of the rare earth material in alumina and the high sputter efficiency of the rare earth doped alumina suggest that practical formation of a sputter target material proceed through a first step of alloying the rare earth dopant and one or more of the host oxide additions to form a first material. The remainder of the host materials can be added prior to consolidation of the alloy target material. With this understanding the practitioner can fabricate alloy tiles of uniform composition having the benefit of dissolved rare earth dopant distribution. Methods for producing tiles to form target 12 is further discussed below.

[0072] In some embodiments, metallic target material can be prepared by atomizing rare-earth atoms with host atoms. For example, Er and/or Yb can be atomized with Al to form pre-alloyed powders which can be utilized to form targets. FIG. 4B shows a phase diagram of Er and Al ions. The phase diagram shows various compounds of Al and Er formed. At the typical compositions of Er utilized in formation of erbium-doped amplifier structures (e.g., up to 1.5 cat % erbium concentration in the amplifier), Al₃Er is formed.

[0073] In several embodiments of the invention, material tiles are formed. These tiles can be mounted on a backing plate to form a target for apparatus 10. FIG. 3A shows an embodiment of targets 12 formed with individual tiles 30 mounted on a cooled backplate 25. In order to form a wide area target of an alloy target material, the consolidated material of individual tiles 30 should first be uniform to the grain size of the powder from which it is formed. It also should be formed into a structural material capable of forming and finishing to a tile shape having a surface roughness on the order of the powder size from which it is consolidated. As an example, the manufacture of indium tin oxide targets for wide area deposition has shown that it is impractical to attempt to form a single piece, wide area target of fragile or brittle oxide material. The wide area sputter cathode is therefore formed from a close packed array of smaller tiles. Target 12, therefore, may include any number of tiles 30, for example between 2 to 20 individual tiles 30. Tiles 30 are finished to a size so as to provide a margin of non-contact, tile to tile, 29 in FIG. 3A, less than about 0.010″ to about 0.020″ or less than half a millimeter so as to eliminate plasma processes between adjacent ones of tiles 30. The distance between tiles 30 of target 12 and the dark space anode or ground shield 19, in FIGS. 1A and 1B can be somewhat larger so as to provide non contact assembly or provide for thermal expansion tolerance during process chamber conditioning or operation.

[0074] The low thermal expansion and fragile condition of ideal optical dielectric tile material can be a cause of great difficulty in bonding and processing a wide area array of tiles 30. The bonding process that overcomes these difficulties is illustrated in FIG. 3A. Sputter coating a side of each of tiles 30 in region 26 prior to bonding with backing plate 25 can be accomplished with a layer of a material such as chrome or nickel as a diffusion layer. Such a metallurgical layer acts as a wetting layer to be tinned with a suitable solder material such as indium or an indium alloy. Backing plate 25 can be made of titanium or molybdenum or other low expansion metal so as to provide a good match with the thermal expansion of the material of tiles 30. A substantial aspect of the formation of a tiled target is the finishing and coating of the backing plate prior to the solder bonding of the array of tiles. The portion 27 of the backing plate to be exposed to vacuum, either between adjacent ones of tiles 30 or about the periphery or dark space region 27 of target 12 should be bead blasted or otherwise etched and plasma spray coated with a material such as alumina or silica to prevent contamination of the process by the target backing plate material. The portion 26 of the backing plate beneath each of tiles 30 can be sputter coated with a material such as nickel or chrome to enable solder bonding. Pure indium solder, although it has a higher melting point than alloys such as indium-tin, is much more ductile and allows the solder to yield during cooling of the solder bonded assembly relieving stress on the bonded tiles 30.

[0075] It is useful to provide an outer frame fixture which is located precisely for the location of the outer tiles. It is also useful to provide shim location, tile to tile, while the assembly is at temperature. The actual solder application and lay up procedure can be devised by those versed in solder assembly. To enhance heat transfer, the solder can form a full fill of the volume between each of tiles 30 and backing plate 25. In order to prevent contamination of the plasma in apparatus 10, the solder not be exposed to the plasma. There should not be any visible solder in the region between adjacent tiles 30 or on backing plate 25. It is, then, useful to sputter coat the wetting layer area with an offset 28 of several millimeters on both tile 30 and backing plate 25. It is also useful to pre-solder or tin both tiles 30 and backing plate 25 prior to final assembly. The solder material should not wet region 28 upon assembly. A mask for sputter deposition of the diffusion barrier/wetting layer film can be useful in this process. Finally, cleaning of the bonded target tile assembly should utilize anhydrous cleaning rather than aqueous based cleaning methods to prevent contamination of the material of tiles 30 with water.

[0076] In accordance with the present invention, target tiles with pre-alloyed rare-earth impurity ions are formed. Pre-alloyed targets can be formed either as metallic targets or ceramic targets. Rare-earth doped material films can then be deposited on substrate 16 of FIGS. 1A and 1B.

[0077]FIG. 3B shows a planar view of an embodiment of target 12 appropriate for an AKT-1600 system. Target 12 in FIG. 3B is appropriate for ceramic targets according to the present invention. Since tiles for metallic targets can be made larger in size, fewer of them are required to form target 12 (for example, 9 instead of 20). Target 12 of FIG. 3B shows 20 tiles 30 mounted on backing plate 25. Tiles 30 are cut and machined to appropriate shapes and sizes for mounting on backing plate 25. In FIG. 3B, for example, each of tiles 30 can be of dimension 134.53×145.05 mm, with tiles 30 in the corner rounded with a radius R of 67.82 mm. The separation between tiles is about 0.76 mm. The total target size is about 675.70×582.48 mm. Target 12 in general can include any number of tiles 30.

[0078]FIG. 4C shows an example of a waveguide amplifier deposited with apparatus 10 utilizing a target according to the present invention. A first cladding layer can be deposited on substrate 16 utilizing a target 12 with substantially no erbium content. Substrate 16, in most cases, is a silicon substrate. An active core 40 can then be deposited and patterned to form a waveguide. Deposition of the material layer to form the active core 40 can be formed utilizing an erbium containing target 12 according to the present invention. Finally, a second cladding layer 403 can be formed over core 40. Both pump and signal light can be coupled into core 402. First cladding layer 401 and second cladding layer 403 are often much thicker than core 402. The resulting amplified signal can be measured as it exits core 402. The amplifier can be described by its width W, thickness T and length L as is illustrated in FIG. 4. Cladding layers 401 and 403 can be formed in any fashion, for example as described in either of the '050 application or the '245 application. Core 402 is deposited utilizing targets according to the present invention. Ceramic Targets

[0079]FIG. 5 illustrates an embodiment of a method 500 to manufacture of one of tiles 30 for target 12 according to the present invention. The resulting target produced by the method illustrated in FIG. 4 is a ceramic target.

[0080] In step 501, several oxide materials are mixed in a dry mixing process. The oxide materials can include host oxides such as SiO₂ and Al₂O₃, for example, and rare earth oxides such as Er₂O₃ and Yb₂O₃, for example. The relative concentrations of materials can be tailored for the particular film to be deposited on substrate 16 (FIG. 1A) with the resulting target. In some embodiments, starting materials with small particle sizes (a few microns or less) are utilized. In some materials, de-agglomerated power (especially for Al₂O₃ and SiO₂) to prevent cracking of the target due to agglomerates can be utilized.

[0081] Higher rare earth concentrations, for example higher Er concentrations, can result in better sintering of the resulting ceramic tiles. However, the Er concentrations in the resulting deposited layer on substrate 16 (FIG. 1A) will also be increased. Erbium ion concentrations above a particular level may serve to quench the gain of a resulting erbium amplifier based on the deposited film. Through up-conversion processes and other dilatory processes, pump radiation may be absorbed into processes that do not contribute to amplification of signal light in the amplifier. Up-conversion, for example, is a dipole-dipole processes which is dependent on the sixth power of the separation between adjoining Er pairs. The closer the Er ions are to each other, then, the larger is the amount of up-conversion and the higher the required pump-power to attain sufficient gain in a resulting amplifier. A concentration of about 3×10²⁰ atoms/cm³ uniformly distributed in the deposited material results in an interatomic separation between adjoining Er atoms of about 14 Å. In general, the interatomic separation is proportional to the cube root of the inverse of the atomic concentration. As has been discussed above, it is difficult to prevent the erbium ions to cluster (i.e., forming either pairs or larger erbium groups). In accordance with the present invention, target materials include alloyed compounds of erbium, which helps to prevent the clustering of erbium ions on deposition.

[0082] Typically, the oxide materials are high purity oxides combined together in particular ratio compositions in order to achieve the final target composition, which result in a particular composition of deposited materials. In some embodiments, the oxide materials are combined such that the mixed powder includes up to about 10% by cation concentration of rare earth atoms. The combined oxide materials are then mixed until the various oxide materials are uniformly distributed throughout the mixed powder.

[0083] Any mixing method which uniformly mixes the powders can be utilized in mixing step 501. In some embodiments, the oxide materials are placed in a barrel mixer with mixing balls, for example about 2 cm diameter zirconia balls, over a long period of time, for example about 4 to about 24 hours, in order that each constituent oxide material is uniformly distributed throughout the resulting mix. The barrel mixer turns with the balls and the combined material, evenly distributing each of the component materials and breaking up any aggregation of component materials. The zirconia balls can be filtered from the mixture after the mixing process. Dry mixing can, for example, reduce the amount of OH impurities present in the finished tile. Further, in some embodiments dry mixing and utilization of oxide materials that do not agglomerate (e.g., which have anti-agglomeration agents mixed with the component materials) can be utilized. Aggregated materials, for example, Al₂O₃ clusters, can cause weak points in the target where the target may crack during use and further can result in non-uniform material deposition.

[0084] Once the material is mixed in step 501, it is cold pressed in step 502. In a typical cold pressing process, the mixed material from step 501 is placed in a rubber mold of an appropriate size and pressed at room temperature at a pressure sufficient to reduce the density of the mixed material to about 50-60% that of the theoretical density to form a green billet. In some embodiments, a pressure higher than about 30 kpsi can be applied to form the green billet.

[0085] In step 503, the green billet is degassed. In some embodiments, the green billet is placed in a mild steel mold lined with graphoil during de-gassing. For example, the green billet formed from the specific mixture described above can be de-gassed at a temperature above about 500 C in a vacuum (about 10⁻⁶ Torr) for a period of time, for example up to about 10 hours. In some embodiments, de-gassing can also remove de-agglomerate agents which may have been included with the starting powders, as well as removing some contaminants, for example water, from the green billet. Typical degass steps in conventional HIPing processes utilize temperatures below about 400° C. Therefore, the method of forming target tiles 30 according to the present invention involves a degas step significantly above that utilized in conventional processes.

[0086] When de-gassing step 503 is complete, the green billet can be hot-isostatically pressed (HIPed) in step 504, at high temperature and high pressure to form the billet. The degassed green billet is sealed into the mild steel mold and heated subjected to conditions of high temperature and high pressure. In one example, the tile is HIPed at a temperature less than about 1000° C. and a pressure higher than about 20 Kpsi. The billet is cooled very slowly to avoid cracking the billet. Cooling over about a 2 day period may be necessary.

[0087] The combination of high temperature de-gas and hot isostatic pressing results in a billet of material where rare-earth ions are alloyed with the host materials. Erbium ions, for example, form compounds of erbium, aluminum and oxygen. Ytterbium typically forms compounds with silicon and oxygen. In deposition, therefore, erbium ions are deposited on substrate 16 as part of the alloyed compound rather than an independent atomic species, which is much more likely to cluster with other erbium ions during deposition. Clustering of erbium, for example, in deposition results in a degraded performance of a resulting optical device. Relatively little of the erbium and ytterbium remains unalloyed with the alumina and silica of the ceramic materials. Low temperature de-gassing has not been found to be effective in forming alloyed billets of erbium and ytterbium.

[0088] In step 505, the billet is finished, which can involve cutting to size and machining to final dimensions to form individual tiles 30 as shown in FIG. 3A. Once the tile is formed, it can be mounted on a target backing 25 as described with FIG. 3A and provided as part of target 12 for use in apparatus 10. The resulting tile has Erbium in solution with Aluminum with few to no aggregates of Al₂O₃ or Er₂O₃ in the tile. In addition, the resulting target tile includes substantially no rare-earth oxides, with substantially all of the rare-Earths being alloyed with the SiO₂ or Al₂O₃. In most examples, Er₂O₃ combines with Al₂O₃ form the alloyed material ErAlO₃ and Yb₂O₃ combines with SiO₂ to form Yb₂Si₂O₇. Other alloyed compounds, for example Er₂SiO₅, may also be formed. Substantially all of the Er₂O₃ and Yb₂O₃ components have been alloyed in the resulting tile. In some embodiments, some small concentration of one of Er₂O₃ and Yb₂O₃ components may remain in the tile.

[0089] In summary, predetermined relative concentrations of host oxides and rare-earth oxides are mixed in step 501 such that each of the individual components is uniformly distributed through the powder. Mixing in a barrel mixer with zirconia balls for a time greater than about 4 hours suffice to thoroughly mix the constituents. The constituents, further, may be mixed with anti-aggregation agents to aid in insuring the each of the constituents are uniformly distributed. In some embodiments, the constituent oxides can include SiO₂, Al₂O₃, Er₂O₃ and Yb₂O₃ in any relative concentrations such that the erbium becomes prealloyed. In some embodiments, the relative concentration of rare earths may be as high as about 10 cat. %.

[0090] Once mixed, the mixed powder is formed by CIPing. The formed powder is then placed in a steel form and degassed in vacuum at a temperature greater than about 500° C. The steel container is then sealed and the powder is HIPed at high temperature, e.g. about 1000° C., and at high pressure, e.g. about 30 Kpsi, to form individual tiles 30. Several of the individual tiles 30 can then be mounted on a backing 25 to form target 12.

[0091] In some embodiments, a pre-alloyed powder for a ceramic target can be formed in an Al₂O₃ crucible by e-beam melting of a solution of Al₂O₃, Er₂O₃, Yb₂O₃, and SiO₂, for example. For example, E-beam evaporation of Silicon oxide and Erbium oxide using 2 e-beam guns as been accomplished by the inventors. The process for evaporation of a metal film usually includes either aluminum oxide and molybdenum crucibles for holding and melting the starting materials. A Molybdenum crucible was selected to hold the oxides because molybdenum has a higher melting temperature than Aluminum oxide. The deposited film of silicon oxide doped with erbium oxide was characterized for photoluminescence and lifetime. The lifetime is estimated to be about 1 ms. In order to increase the lifetime and photoluminescence the solubility of Erbium oxide has to be increased in a host like aluminum oxide. Therefore, if an aluminum oxide crucible is utilized in the evaporation process, it is expected that the erbium ions will pre-alloy with the crucible material. The material in the crucible can then be crushed into a powder for formation into tiles appropriate for a ceramic target by HIPing.

[0092] High purity starting materials can be purchased from several manufacturers. For example, SiO₂ that is 99.99% pure and has a particle size of between about 0.02 and about 0.55 microns can be obtained from Pred Materials, New York, N.Y. Al₂O₃ that is 99.999% pure and has an average particle size of about 0.49 microns can be obtained from Ceralox, Tucson, Ariz. Yb₂O₃ that is 99.99% pure and has a particle size of about 3 microns can be obtained from Stanford Materials. Er₂O₃ that is 99.999% pure and has an average particle size of about 9 microns can be obtained from Stanford Materials, Aliso Vlejo, Calif.

[0093] In some embodiments, targets formed in this fashion 6 can include up to about 37% Al₂O₃, about 57.0% SiO₂ or less, about 2.5% of Er₂O₃ or less, and about 2.5% of Yb₂O₃ or less.

[0094] Several specific examples of embodiments of targets with ceramic tiles are discussed below. Further, examples of optical amplifiers produced utilizing the ceramic tiles according to the present invention are presented. These examples are provided for illustrative purposes only and are not intended to be limiting.

EXAMPLE 1

[0095] One example embodiment of the invention utilizes starting materials in the concentration of SiO₂/Al₂O₃/Er₂O₃/Yb₂O₃ being 57.5/37.5/2.5/2.5 cat % (the “2.5/2.5 target”). As described in step 501, the oxide materials are combined in the proportion stated above and mixed in a barrel mixer with 2 cm diameter zironcia balls for between about 8 and 24 hours. As described in step 502, the resulting mixture is poured into rubber pouches and cold pressed to appropriate size for making tiles. In some embodiments, the finished tile size is about 5.711×5.296×4 mm in size. The cold pressing step reduces the density of the material to about 50 to 60% of the theoretical density to form the green tile. As described in step 503, the green billet is then placed in a mild steel mold which has been lined with non-stick graphite and degassed in vacuum at about 650C for about 6 to 10 h. The green billet is then sealed into the mild steel canister and HIPed at a temperature of about 1000C and a pressure of about 28.5 Kpsi, as described in step 504 to form a billet. In step 505, the billet is cut and machined to the dimensions described above to form a tile.

[0096] FIGS. 6A-6F shows x-ray diffraction spectrum taken from a tile produced as described in this Example. As shown in FIGS. 6A through 6F, the tile includes ErAlO₃, Yb₂Si₂O₇, Er₂SiO₅, Yb₂O₃, Al₂O₃ and SiO₂ but substantially no Er₂O₃. FIGS. 6A through 6F point out the x-ray spectrum from ErAlO₃, Yb₂Si₂O₇, Er₂SiO₅, Yb₂O₃, Al₂O₃ and SiO₂. In other words, all of the erbium has been alloyed with Aluminum and Silicates. FIGS. 6G and 6H show EDX data (Electron Dispersion Spectroscopy) which also show Er and Yb alloying with Al and Si oxides.

[0097] The resulting tiles 30 formed in the above described procedure can then formed on a backing 25 to form a ceramic target 12. Positioning about 20 of tiles 30 onto backing 20 results in a target 12 with dimensions of about 675.70×582.48×4 mm (neglecting the thickness of backing 25). Tiles 30 are mounted on backing plate 25 as is described with FIG. 3.

[0098] Target 12 formed by this example can then be mounted in apparatus 10 and utilized to form an optical amplifier layer. Material from target 12 may be deposited onto a substrate held at T=350C with an RF power at 13.56 MHz of 2000W and a sputtering gas flow of 40 sccm of Ar. Substrate 16 is a silicon substrate. No bias is applied to substrate 16 (i.e., substrate 16 is grounded) and no lower frequency power is applied to target 12. The spacing betwee substrate 16 and target 12 is 6 cm. The magnet is swept at a rate of 4 s/scan.

[0099] A material layer of thickness about 0.8 μm can then be formed. The Er concentration, which can be verified by EDS (electron dispersion spectroscopy) corresponds to about 7×10²⁰ atoms/cm³ (which is the highest Er concentration reported to date). Similarly, the Yb concentration corresponds to about 7×10²⁰ atoms/cm³.

[0100] For measurement purposes, the film deposited from target 12 can be etched to form an active core of about 5 μm wide and about 1.1 cm in length. A cladding layer can then be deposited over the active waveguide. Substrate 16 is then annealed at 800 C for about 30 min. Signal and pump light can be coupled into the active core in order to measure amplifier parameters.

[0101] The core material has an as-deposited refractive index of about 1.563, which becomes 1.5497 after annealing. The deposited cladding layers 401 and 403 (see FIG. 4) have an index of 1.445. The net Gain of the amplifier formed is about 2.8 dB/1.1 cm, which corresponds to a gain of 2.5 dB/cm, at an internal pump power of about 30 mW and wavelength of 980 nm and input signal power of about −15 dBm and wavelength 1550 nm. The Er transition lifetime is about 5 ms. The upconversion coefficient is about 1.4×10⁻¹⁷ cm³/s.

EXAMPLE 2

[0102] Another example embodiment of the invention utilizes starting materials in the concentration of SiO₂/Al₂O₃/Er₂O₃/Yb₂O₃ being 54.5/44.5/1.0/0.0 cat % (the “1/0 target”). The starting oxide materials are the same as those described with Example 1. As described in step 501, the oxide materials are combined in the proportion stated above and mixed in a barrel mixer with 2 cm diameter zironcia balls for between about 8 and 24 hours. As described in step 502, the resulting mixture is poured into rubber pouches and cold pressed to appropriate size for making tiles. In some embodiments, the finished tile size is about 5.711×5.296×4 mm in size. The cold pressing step reduces the density of the material to about 50 to 60% of the theoretical density to form the green tile. As described in step 503, the green tile is then placed in a mild steel mold which has been coated with non-stick graphite and degassed in vacuum at about 650C for about 6 to 10 h. The green tile is then sealed into the mild steel canister and HIPed at a temperature of about 1000C and a pressure of about 28.5 Kpsi, as described in step 504.

[0103]FIGS. 7A through 7D show x-ray diffraction data for this example with the individual peaks for ErAlO₃, Er₂SiO₅, Al₂O₃, and SiO₂, respectively, identified. The target material according to this example includes ErAlO₃, Er₂SiO₅, Al₂O₃, and SiO₂, but substantially no Er₂O₃. Again, the erbium is completely alloyed into the Al₂O₃ and SiO₂ host with little to no free Er₂O₃ present in the finished tile 30 for target 12.

[0104] The resulting tiles 30 formed in the above described procedure can then formed on a backing 25 to form a ceramic target 12. Positioning about 20 of tiles 30 onto backing 20 results in a target 12 with dimensions of about 675.70×582.48×4 mm (neglecting the thickness of backing 25). Tiles 30 are mounted on backing plate 25 as is described with FIG. 3.

[0105] Target 12 formed by this example can then be mounted in apparatus 10 and utilized to form an optical amplifier layer. Material from target 12 may be deposited onto a substrate held at T=200 C with an RF power at 13.56 MHz of 2.5 kW and a sputtering gas flow of 60 sccm of Ar. No bias is applied to substrate 16 (i.e., substrate 16 is grounded) and no lower frequency power is applied to target 12. Separation between substrate 16 and target 12 is about 6 cm. The magnet is swept at a rate of about 4 s/scan.

[0106] A material layer of thickness about 1.17 μm can then be formed. The Er concentration, verified by EDS, corresponds to about 2.9×10²⁰ atoms/cm³.

[0107] For measurement purposes, the film deposited from target 12 can be etched to form an active core about 5-6 μm wide and about 1.6 cm in length. A cladding layer can then be deposited over the active waveguide. The sample is then annealed at 725 C for 30 min. Signal and pump light can be coupled into the active core in order to measure amplifier parameters.

[0108] The net gain of the resulting amplifier is about 17 dB/20 cm at an internal pump power of about 260 mW, pump wavelength of 976 nm and input signal of about −20 dBm at 1550 nm. The Er transition lifetime is about 2.9 ms. The upconversion coefficient is about 4.5×10⁻¹⁸ cm³/s.

EXAMPLE 3

[0109] Another example embodiment of the invention utilizes starting materials in the concentration of SiO₂/Al₂O₃/Er₂O₃/Yb₂O₃ being 54.0/44.6/1.0/0.4 cat % (the “1/0.4 target”). The starting oxide materials are the same as those described with Example 1. As described in step 501, the oxide materials are combined in the proportion stated above and mixed in a barrel mixer with 2 cm diameter zironcia balls for between about 8 and 24 hours. As described in step 502, the resulting mixture is poured into rubber pouches and cold pressed to appropriate size for making tiles. In some embodiments, the finished tile size is about 5.711×5.296×4 mm in size. The cold pressing step reduces the density of the material to about 50 to 60% of the theoretical density to form the green tile. As described in step 503, the green tile is then placed in a mild steel mold which has been coated with non-stick graphite and degassed in vacuum at about 650C for about 6 to 10 h. The green tile is then sealed into the mild steel canister and HIPed at a temperature of about 1000C and a pressure of about 28.5 Kpsi, as described in step 504.

[0110] The resulting tiles 30 formed in the above described procedure can then formed on a backing 25 to form a ceramic target 12. Positioning about 20 of tiles 30 onto backing 20 results in a target 12 with dimensions of about 675.70×582.48×4 mm (neglecting the thickness of backing 25). Tiles 30 are mounted on backing plate 25 as is described with FIG. 3.

[0111] Target 12 formed by this example can then be mounted in apparatus 10 and utilized to form an optical amplifier layer. Material from target 12 may be deposited onto a substrate held at T=350° C. with an RF power at 13.56 MHz of 2.0 kW and a sputtering gas flow of 60 sccm of Ar. Substrate 16 is biased with about 100 W of 1.2 MHz RF power. The separation between substrate 16 and target 12 is about 6 cm. The magnet is swept at a rate of 4 s/scan. The formed amplifier is annealed at 800 C for 30 minutes.

[0112] A material layer of thickness about 1.2 μm can then be formed. The Er concentration, verified by erbium dispersion spectroscopy, corresponds to about 2.9×10²⁰ atoms/cm³.

[0113] For measurement purposes, the film deposited from target 12 can be etched to form active cores of between 2 and 5 μm wide and about 9.1 cm in length. A cladding layer can then be deposited over the active waveguide. The sample can then be annealed at 800 C for 30 minutes. As shown in FIG. 4, a bottom cladding layer 401 of thickness approximately 15 μm and a top cladding layer 403 of approximately 10 μm can be deposited.

[0114] Signal and pump light can be coupled into the active core in order to measure amplifier parameters. The waveguide formed in this manner can be double pumped (i.e., pumped forward and backward through the waveguide) with a 976 nm pump at 250 mW in the forward direction and a 974 nm pump at 147 mW in the backward direction. The resulting gain is about 3.8 dB with a 1530 nm signal at input power of −20 dB. The up-conversion constant for this deposited layer is about 5.61×10⁻¹⁸ cm³/s and the lifetime of the erbium states is about 3.29 ms.

Metallic Targets

[0115] Metallic targets tend not to be as brittle as the Ceramic targets discussed above and therefore tiles 30 can be formed in larger sizes. Metallic targets can also be utilized for higher sputtering rates than ceramic targets. A fewer number of tiles 30, therefore, may be necessary to form target 12. In addition, in some embodiments metallic constituents can be plasma sprayed or flame sprayed directly onto backing 25 with the necessity of forming tiles 30 through the HIPing process.

[0116]FIG. 8A shows an embodiment of a method 800 of fabricating one of tiles 30 of target 12 according to the present invention. In step 801, constituent powders are pre-alloyed in an atomization process. In some embodiments, rare earth ions are alloyed with aluminum, for example. In an atomization process, liquid is broken up into fine drops. The desired metal composition of host with rare-earth material (e.g., aluminum with erbium and ytterbium) is inserted into a vacuum induction furnace and brought to a temperature of about 1500° C. The molten material is then poured into a tundish where it is rapidly cooled by argon flow. A solid powder is formed which has compounds of the rare-earth components with the host material.

[0117] In general, metallic targets can be formed with a combination of any metallic or semiconductor material and rare earths. For example, target 12 can have any composition and can include ions other than Si, Al, Er and Yb, including: Zn, Ga, Ge, P, As, Sn, Sb, and Pb and rare earths Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy Ho, Er, Tm Yb and Lu.

[0118] In step 802, the pre-alloyed powder can be mixed. Further, other component materials such as, for example, Si can be added during step 802. In some embodiments, the constituent powders are mixed in a barrel mixer for some time, for example between 2 and 8 hrs, with large (about 2 cm diameter) zirconia balls.

[0119] In some embodiments, the mixed power formed in step 802 can include up to about 35% of Al, about 65% Si or less, about 1.0% of Er or less and about 1.0% Yb or less.

[0120] Since the packing density of metallic powders is in general higher than ceramic powders, no CIPing process is required with metallic targets. However, some embodiments of the invention may include a separate CIPing step similar to that described in the formation of ceramic targets according to the present invention.

[0121] In step 803, the material is degassed in vacuum. In some embodiments of the process, the mixed powder is placed into a mild steel canister lined with graphoil and heated in a vacuum. In some embodiments, the degass process occurs at a temperature of about 400 C at a pressure of about 10⁻⁶ Torr range. In step 804, the mild steel canister can be sealed in vacuum and the material HIPed at low temperature to form a billet In some embodiments, HIPing can be performed at temperatures above about 450 C and pressures above about 15 Kpsi for longer than about 1 hour. If, after HIPing step 904, the billet is cooled too slowly, the billet may be non-alloyed. Therefore, the billet should be cooled in a time less than about 5 hours to avoid Er precipitation. Note that cooling too fast may result in cracking of the billet. The billet is typically cooled to room temperature in about 2 to 3 hours.

[0122] In step 805, the billet can be cut and machined to form tiles 30. In some embodiments, tiles 30 of the size 213.91×182.91×4 mm are produced. Tiles 30 according to this embodiment can be formed into target 12 as is described with FIG. 3.

[0123] Pre-alloying of tiles 30 can be shown with x-ray diffraction data taken on powders formed by the prealloying step 801 of method 800. In embodiments where Er and Yb are prealloyed with Al in step 801, x-ray diffraction data typically shows Al₃Er, Al₃Yb, and Al in the powder before mixing with a very small to substantially no concentration of free Er. In some embodiments, the alloyed powder from step 801 is mixed with Si in step 902 in order that the final powder mixture is appropriate for the material. In some embodiments, total rare-earth ion concentrations are up to about 5 cat %. The resulting deposited material layer, then, has a uniform distribution of Er and, because aggregates are reduced, target 12 can be longer lasting.

[0124] Rare earth elements can be obtained from Stanford Materials, Aliso Vlejo, Calif. Ceram Research can provide Aluminum of the appropriate purity. Si powder can be provided from Noah Technologies Corporation, San Antonio, Tex.

[0125] The overall purity of materials can be approximately 99.99% pure. Special care can be taken to reduce the concentration of transition metals included, for example to no more than a few ppm and the concentration of hydrogen. Both transition metals and OH impurities in target 12 can act as photoluminesance quenchers, which detract from the performance of an amplifier produced with target 12.

[0126]FIG. 8B shows another method 910 of forming target 12. Instead of producing tiles 30 and mounting tiles 30 onto backing 25 as is described with respect to FIG. 3A, the mixed powder can be plasma sprayed directly onto backing 25. In method 810, powder pre-alloy 801 and mixing 802 are the same as in method 800 of FIG. 8A. In step 813, however, the mixed powder is plasma sprayed in an inert atmosphere directly onto backing plate 25. In some embodiment, the resulting coating on backing plate 25 can be as thick as about 1.5 mm and as dense as about 95% of the theoretical density. Method 810 of FIG. 8B may be a very fast and simple process for forming metallic targets without the need for tiles. Another advantage is an extremely fast cooling rate, which avoids erbium precipitation from the intermetallics during cooling.

EXAMPLE 4

[0127] A target tile with composition Si/Al/Er/Yb being 57.4/41.0/0.8/0.8 cat % (the “0.8/0.8 target”) can be produced by the above method. The proper proportional amounts of Al, Er and Yb powder are placed in the vacuum induction furnace in step 801 and heated to about 1500° C. The atomized powder is mixed with the proper proportional amount of Si in mixing step 802. The powders are mixed in a barrel mixer for about 4 hours with large zironcia balls (approximately 2 cm in diameter). In step 802, the mixed powder is poured into a rubber mold of the right size to produce finished tiles of the size 213.91×182.91×4 mm. Nine (9) such tiles will form a target for apparatus 10 of FIG. 1A. The formed powder is inserted into a mild steel canister and degassed at about 400 C in a vacuum (about 10⁻⁶ Torr) in step 803. The degassed tile is then sealed into the steel canister and HIPed at low temperature and high pressure (about 600 C at 20 Kpsi for about 4 hours) to form billets. The billets are then cut and machined to size in setp 805. The individual tiles 30 are mounted as is described with FIG. 3A to form target 12.

[0128]FIG. 9 shows an x-ray diffraction spectrum of the atomized powder before mixing step 902 is performed. As is shown in FIG. 10, compounds of YbAl₃, Al₃Er, and Al are present but substantially no free Er or Yb are observed. This shows that virtually all of the rare-earth compounds are alloyed with the aluminum during the atomization process. Target 12 produced according to this example results in Yb—Al, Er—Al, Yb—Si, and Er—Si alloys but found substantially no free Er.

[0129] In formation of an amplifier utilizing target 12 of this Example, an undercladding layer 401 is deposited with about 10 μm thickness, then a layer can be deposited utilizing target 12 according to this example and patterned to form a core 402. Then a second cladding layer of about 10 μm thickness 403 is formed over core 402. The amplifier can then be annealed at about 725 C for about 30 min.

[0130] A film of material from which core 402 can be formed can be deposited in apparatus 10 using the 0.8/0.8 target as target 12. A pulsed DC power is applied through power supply 15 to the target. About 6 KW of 120 KHz pulsed DC power is supplied. Substrate 16 is biased with about 100 W of 2 MHz frequency power. An argon gas flow at 60 sccm and an oxygen gas flow at about 28 sccm is supplied to reactor apparatus 10. The deposited layer can be of any thickness, for example 1.1 μm

[0131]FIG. 10B shows an SEM of a cross section of a 3.5 μm wide waveguide formed utilizing target 12 according to this Example and the deposition process described above. FIG. 10B shows core 402 deposited with target 12 according to the present Example and cladding layers 401 and 402. Core 402 is deposited at a 1.1 μm thickness.

[0132] The deposition results in an erbium and ytterbium concentrations of about 2.3×10²⁰ cm⁻³. The resulting up-conversion coefficient is 5×10⁻¹⁸ cm³/s and the erbium excited state lifetime is about 3 ms. At an internal pumping power of about 200 mW at a wavelength of 982 nm and with an input signal of about −28 dBm, the internal gain across the C-band is aobut 8.9 dB for a 10.1 cm amplifier produced according to this example. The power level of 1060 nm signal light in FIG. 10C is about −25 dB and the power level of signal light in FIG. 10D is 0 dB.

EXAMPLE 5

[0133] A target tile with composition Si/Al/Er/Yb being 57.4/41.0/1.5/0.0 cat % (the “1.5/0.0 target”) can be produced by the above method. The proper proportional amounts of Al, and Er powder are placed in the vacuum induction furnace in step 801 and heated to about 1500° C. The atomized powder is mixed with the proper proportional amount of Si in mixing step 802. The powders are mixed in a barrel mixer for about 4 hours with large zironcia balls (approximately 2 cm in diameter). In step 803, the mixed powder is poured into a rubber mold of the right size to produce finished tiles of the size 213.91×182.91×4 mm and degassed at about 400 C in a vacuum (about 10⁻⁶ Torr). In step 804, the degassed billet is then sealed into the steel canister and HIPed at low temperature and high pressure (about 600 C at 20 Kpsi for about 4 hours) to form a billet. In step 805, the billets are cut and machined to size to form a tile. The individual tiles 30 are mounted as is described with FIG. 3 to form target 12.

[0134]FIG. 10 shows x-ray diffraction data of the power formed in step 802 of this example. The x-ray diffraction data shows the existence of Er_(x)Si_(y) and Er_(x)Al_(y) alloys with Al and Si.

[0135] In producing an amplifier waveguide, an under cladding layer 401 is first deposited. The under cladding layer is of thickness around 10 μm. Then a layer of material utilizing target 12 of the present example is deposited and patterned to form a core 402. Finally, an upper cladding layer of thickness around 10 μm is deposited. The cladding layers can be deposited in any fashion, for example as is described in the '050 application or the '245 application.

[0136] The material layer utilized for forming core 402 is, in this example, deposited using the 1.5/0 target described above. Six (6) KW of pulsed DC power at 120 KHz is applied to target 12. The reverse pulsing time is 2.3 μs. One hundred (100) watts of bias power at 2 MHz bias frequency is supplied to substrate 16. Gas flows of 60 sccm of Ar and 28 sccm of oxygen is flowed through the reaction chamber of apparatus 10. The amplifier is annealed at a temperature of 725 C for 30 min.

[0137] The up conversion constant Cup is measured to be about 8.0×10⁻¹⁸ cm³/s with a lifetime at 1530 nm is about 1.55 ms. The internal gain across the C-band is about 13.7 dB in a 10.1 cm waveguide double pumped with 978 nm light at an internal pumping power of around 150 mW. The erbium concentration is about 4.5×10²⁰/cm³.

[0138] The examples and embodiments discussed above are exemplary only and are not intended to be limiting. One skilled in the art can vary the processes specifically described here in various ways. Further, the theories and discussions of mechanisms presented above are for discussion only. The invention disclosed herein is not intended to be bound by any particular theory set forth by the inventors to explain the results obtained. As such, the invention is limited only by the following claims. 

We claim:
 1. A method of forming a target for deposition chamber, comprising: forming a pre-alloyed material with at least one rare-earth ion alloyed with at least one host material; forming the target from the pre-alloyed material.
 2. The method of claim 1, where forming a pre-alloyed material includes mixing at least one rare-earth oxide material with at least one host oxide to form mixed material; forming a green billet from the mixed material; degassing the green billet to form a de-gassed green billet; pressing the de-gassed green billet at high temperatures to form a billet of the pre-alloyed material.
 3. The method of claim 2, wherein pressing the de-gassed green billet at high temperature includes applying a pressure higher than about 20 Kpsi and temperature less than about 1000 C for a time greater than about 1 hour.
 4. The method of claim 2 wherein degassing the green billet includes heating the green billet includes heating the green billet to a temperature greater than about 500 C.
 5. The method of claim 2, wherein mixing at least one rare-earth oxide material with at least one host oxide includes barrel mixer in relative concentrations such that the rare-earth ions make up less than about 10 cat. % of the mixed material.
 6. The method of claim 5, wherein the mixed material includes up to about 37% Al₂O₃, about 57.0% SiO₂ or less, about 2.5% of Er₂O₃ or less, and about 2.5% of Yb₂O₃ or less.
 7. The method of claim 6, wherein the mixed material includes about 57.5 cat. % of SiO₂, about 37.5 cat. % of Al₂O₃, about 2.5 cat. % of Er₂O₃, and about 2.5 cat. % of Yb₂O₃.
 8. The method of claim 6, wherein the mixed material includes about 54.5 cat. % of SiO₂, about 44.5 cat. % of Al₂O₃, and about 1.0 cat. % of Er₂O₃.
 9. The method of claim 6, wherein the mixed material includes about 54.0 cat. % of SiO₂, about 44.6 cat. % of Al₂O₃, about 1.0 cat. % of Er₂O₃, and about 0.4 cat. % of Yb₂O₃.
 10. The method of claim 2, wherein forming a green billet includes pressing the mixed material at room temperature.
 11. The method of claim 10, wherein pressing placing the mixed material into a form and applying a pressure greater than about 30 Kpsi to the mixed material.
 12. The method of claim 2, wherein forming the target includes cutting and machining the billet to form tiles; mounting the tiles on a backing plate to form the target.
 13. The method of claim 12, wherein mounting the tiles on a backing plate to form the target includes sputter coating a side of each of a number of tiles to form a diffusion layer; tinning the diffusion layer with a solder material; and soldering the tiles to the backing plate.
 14. The method of claim 1, wherein forming a pre-alloyed material with at least one rare-earth ion alloyed with at least one host material includes atomizing at least one rare-earth ion with at least one metal host to form a pre-alloyed powder; and mixing the pre-alloyed powder to form mixed powder.
 15. The method of claim 14, wherein forming the target from the pre-alloyed material includes flame spraying the mixed powder onto a backing plate.
 16. The method of claim 14, wherein atomizing at least one rare-earth ion with at least one metal host includes atomizing preselected proportions of erbium and ytterbium with aluminum.
 17. The method of claim 14, further including adding silicon to the pre-alloyed powder before barrel mixing.
 18. The method of claim 17, wherein the mixed powder includes up to about 5 cat. % of rare earth ions.
 19. The method of claim 18, wherein the mixed power includes up to about 35% of Al, about 65% Si or less, about 1.0% of Er or less and about 1.0% Yb or less.
 20. The method of claim 19, wherein the mixed powder includes about 57.4 cat. % of Si, about 41.0 cat. % of Al, about 0.8 cat. % of Er and about 0.8 cat. % of Yb.
 21. The method of claim 19, wherein the mixed powder includes about 57.4 cat. % of Si, about 41.0 cat. % of Al, and about 1.5 cat. % of Er.
 22. The method of claim 14, wherein forming the pre-alloyed material includes degassing the mixed powder to form a green billet; pressing the green billet to form a billet of pre-alloyed material.
 23. The method of claim 22, wherein degassing the mixed powder includes heating the powder to a temperature of about 400 C.
 24. The method of claim 23, wherein pressing the green billet includes heating the green billet to a temperature higher than about 450 C at a pressure higher than about 15 Kpsi.
 25. The method of claim 14, wherein forming the target includes cutting and machining the billet to form tiles; and mounting the tiles on a backing plate to form the target.
 26. A target material for a PVD deposition chamber, comprising: at least one host constituent; and at least one rare-earth ion pre-alloyed with some or all of the at least one host constituent.
 27. The target material of claim 26, wherein the host constituent includes at least one metal oxide.
 28. The target material of claim 27, wherein the rare-earth ions make up less than about 10 cat. % of the mixed material.
 29. The method of claim 28, wherein the target material includes more than or equal to about 37% Al₂O₃, less than or equal to about 57.0% SiO₂, less than or equal to about 2.5% of Er₂O₃, and less than or equal to about 2.5% of Yb₂O₃.
 30. The target material of claim 29, wherein the at least one host constituent includes about 57.5 cat. % Of SiO₂ and about 37.5 cat. % of Al₂O₃ and the at least one rare-earth ion includes about 2.5 cat. % of Er₂O₃, and about 2.5 cat. % of Yb₂O₃.
 31. The target material of claim 29, wherein the at least one host constituent includes about 54.5 cat. % Of SiO₂ and about 44.5 cat. % of Al₂O₃ and the at least one rare-earth ion includes about 1.0 cat. % of Er₂O₃.
 32. The target material of claim 29, wherein the at least one host constituent includes about 54.0 cat. % Of SiO₂ and about 44.6 cat. % of Al₂O₃ and the at least one rare-earth ion includes about 1.0 cat. % of Er₂O₃ and about 0.4 cat. % of Yb₂O₃.
 33. The target material of claim 26, wherein the host constituent includes at least one metal.
 34. The target material of claim 33, wherein the rare-earth ions make up about 5 cat % of the mixed material.
 35. The method of claim 34, wherein the target includes more than about 35% of Al, less than about 65% Si, less than about 1.0% of Er and less than about 1.0% Yb.
 36. The target material of claim 35, wherein the at least one host constituent includes about 57.4 cat. % of Si and about 41.0 cat. % of Al and the at least one rare-earth ions include about 0.8 cat. % of Er and about 0.8 cat. % of Yb.
 37. The target material of claim 35, wherein the at least one host constituent includes about 57.4 cat. % of Si and about 41.0 cat. % of Al and the at least one rare-earth ions includes about 1.5 cat. % of Er.
 38. A method of forming a target for a PVD chamber, comprising: melting a mixture containing rare earth ions in an Al₂O₃ crucible; cooling the mixture; forming a power from the cooled mixture; HIPing the powder to form target material; and forming the target from the target material.
 39. The method of claim 38, wherein melting the mixture includes heating with induction heating.
 40. The method of claim 38, wherein melting the mixture includes heating with e-beam heating. 